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Register a new userNonlinear dynamics and chaos in an optomechanical beam
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Added by
Daniel Navarro Urrios
Publication date
2016
fields
Physics
and research's language is
English
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Optical non-linearities, such as thermo-optic effects and free-carrier-dispersion, are often considered as undesired effects in silicon-based resonators and, more specifically, optomechanical (OM) cavities, affecting the relative detuning between an optical resonance and the excitation laser. However, the interplay between such mechanisms could also enable unexpected physical phenomena to be used in new applications. In the present work, we exploit those non-linearities and their intercoupling with the mechanical degrees of freedom of a silicon OM nanobeam to unveil a rich set of fundamentally different complex dynamics. By smoothly changing the parameters of the excitation laser, namely its power and wavelength, we demonstrate accurate control for activating bi-dimensional and tetra-dimensional limit-cycles, a period doubling route and chaos. In addition, by scanning the laser parameters in opposite senses we demonstrate bistability and hysteresis between bi-dimensional and tetra-dimensional limit-cycles, between different coherent mechanical states and between tetra-dimensional limit-cycles and chaos. As a result of implementing the Rosenstein algorithm to the experimental time series we have extracted a Largest Lyapunov Exponent of LLE=1.3x10^5 s-1, which is between one and two orders of magnitude lower than the typical oscillating frequencies of the system. Most of the experimental features can be well reproduced with a model of first-order non-linear differential equations coupled through the number of intracavity photons. Our findings open several routes towards exploiting silicon-based OM photonic crystals for systems with memory and, more specifically, for chaos based applications such as secure information transfer or sensing.
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Non-Hermitian systems exhibit phenomena that are qualitatively different from those of Hermitian systems and have been exploited to achieve a number of ends, including the generation of exceptional points, nonreciprocal dynamics, non-orthogonal normal modes, and topological operations. However to date these effects have only been accessible with nearly-degenerate modes (i.e., modes with frequency difference comparable to their linewidth and coupling rate). Here we demonstrate an optomechanical scheme that extends topological control to highly non-degenerate modes of a non-Hermitian system. Specifically, we induce a virtual exceptional point between two mechanical modes whose frequencies differ by >10^3 times their linewidth and coupling rate, and use adiabatic topological operations to transfer energy between these modes. This scheme can be readily implemented in many physical systems, potentially extending the utility of non-Hermitian dynamics to a much wider range of settings.
Lasers differ from other light sources in that they are coherent, and their coherence makes them indispensable to both fundamental research and practical application. In optomechanical cavities, phonon and photon lasing is facilitated by the ability of photons and phonons to interact intensively and excite one another coherently. The lasing linewidths of both phonons and photons are critical for practical application. However, thus far, these linewidths have not been explored in detail in cavity optomechanical systems. This study investigates the underlying dynamics of lasing in optomechanical cavities and experimentally demonstrates simultaneous photon and phonon lasing with narrow linewidths in a silicon optomechanical crystal cavity. We find that the linewidths can be accounted for by two distinct physical mechanisms in two regimes, namely the normal regime and the reversed regime, where the intrinsic optical decay rate is either larger or smaller than the intrinsic mechanical decay rate. In the normal regime, an ultra-narrow spectral linewidth of 5.4 kHz for phonon lasing at 6.22 GHz can be achieved regardless of the linewidth of the pump light, while these results are counterintuitively unattainable for photon lasing in the reversed regime. These results pave the way towards harnessing the coherence of both photons and phonons in silicon photonic devices and reshaping their spectra, potentially opening up new technologies in sensing, metrology, spectroscopy, and signal processing, as well as in applications requiring sources that offer an ultra-high degree of coherence.
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Optical levitation of mechanical oscillators has been suggested as a promising way to decouple the environmental noise and increase the mechanical quality factor. Here, we investigate the dynamics of a free-standing mirror acting as the top reflector of a vertical optical cavity, designed as a testbed for a tripod cavity optical levitation setup. To reach the regime of levitation for a milligram-scale mirror, the optical intensity of the intracavity optical field approaches 3 MW cm$^{-2}$. We identify three distinct optomechanical effects: excitation of acoustic vibrations, expansion due to photothermal absorption, and partial lift-off of the mirror due to radiation pressure force. These effects are intercoupled via the intracavity optical field and induce complex system dynamics inclusive of high-order sideband generation, optical bistability, parametric amplification, and the optical spring effect. We modify the response of the mirror with active feedback control to improve the overall stability of the system.
The characterization of the complex spatiotemporal dynamics of optical beam propagation in nonlinear multimode fibers requires the development of advanced measurement methods, capable of capturing the real-time evolution of beam images. We present a new space-time mapping technique, permitting the direct detection, with picosecond temporal resolution, of the intensity from repetitive laser pulses over a grid of spatial samples from a magnified image of the output beam. By using this time-resolved mapping, we provide the first unambiguous experimental observation of instantaneous intrapulse nonlinear coupling processes among the modes of a graded index fiber.
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